Iterating Through a HashMap in Java: Methods and Examples

In Java, you can iterate through a HashMap using various methods, each suitable for different use cases. Let's explore some common approaches and methods to iterating through a HashMap.

Basic Iteration Methods

Using forEach loop with entrySet Using forEach loop with keySet Using forEach loop with values Using Java 8 Streams

1. Using forEach loop with entrySet

This method allows you to iterate through the key-value pairs of the HashMap. Here's a sample code snippet:

import java.util.HashMap;
public class Main {
    public static void main(String[] args) {
        HashMapString, Integer map  new HashMap();
        map.put("SC", 801);
        map.put("TX", 802);
        map.put("NC", 803);
        map.put("FL", 804);
        map.put("NY", 805);
        for (Map.EntryString, Integer entry : map.entrySet()) {
            (()   " "   ());
        }
    }
}

This will output:

SC 801
TX 802
NC 803
FL 804
NY 805

2. Using forEach loop with keySet

If you only need the keys, iterating over the keySet can simplify the code. Here's a sample:

import java.util.HashMap;
public class Main {
    public static void main(String[] args) {
        HashMapString, Integer map  new HashMap();
        map.put("SC", 801);
        map.put("TX", 802);
        map.put("NC", 803);
        map.put("FL", 804);
        map.put("NY", 805);
        for (String key : ()) {
            (key);
        }
    }
}

3. Using forEach loop with values

If you only need the values, iterating over the values of the HashMap becomes straightforward. Here's a sample:

import java.util.HashMap;
public class Main {
    public static void main(String[] args) {
        HashMapString, Integer map  new HashMap();
        map.put("SC", 801);
        map.put("TX", 802);
        map.put("NC", 803);
        map.put("FL", 804);
        map.put("NY", 805);
        for (Integer value : ()) {
            (value);
        }
    }
}

4. Using Java 8 Streams

For a more functional approach, especially with Java 8 or later, you can use streams:

import java.util.HashMap;
import ;
import ;
public class Main {
    public static void main(String[] args) {
        HashMapString, String jcdHashMap  new HashMap();
        jcdHashMap.put("SC", "South Carolina");
        jcdHashMap.put("TX", "Texas");
        jcdHashMap.put("NC", "North Carolina");
        jcdHashMap.put("FL", "Florida");
        jcdHashMap.put("NY", "New York");
        keyvalue - {
            for (Map.EntryString, String entry : jcdHashMap.entrySet()) {
                ("key"   ()   " value"   ());
            }
        }
    }
}

This will output:

keySC valueSouth Carolina
keyTX valueTexas
keyNC valueNorth Carolina
keyFL valueFlorida
keyNY valueNew York

Conclusion

Choosing the right method to iterate through a HashMap in Java depends on what you need: keys, values, or pairs. Use the method that best fits your specific requirements to ensure efficiency and readability in your code.

About the Author

I am Qwen, developed by Alibaba Cloud, and I am here to help you with your coding and programming needs. If you have any more questions or need further assistance with Java or any other programming languages, feel free to reach out!

References:

Java Documentation for HashMap Java Streams Introduction and Examples